This invention relates generally to a liquid ink for printers, and more particularly to a liquid ink for printers including a strong alkali material for dissolving at least one of a fibrous material, a sizing material and a surface treatment material included in the recording medium. These inks are particularly wall suited for ink jet-type printers.
In an ink jet-type recording device, printing is accomplished by a print head which produces a minute liquid drop of ink. The ink drop is generally between about 50 and 150 .mu.m in diameter and the print head includes means for ejecting the liquid ink drop to a predetermined position on a recording medium. Severl types of ink jet-type recording devices are available. These include an electrostatic deflection-type jet printer wherein the print head presses and ejects ink through a nozzle orifice having a diameter of about 30 to 150 .mu.m. A charge is applied to the ejected liquid drop which is displaced and positioned on the recording medium selectively by an electric field so that the drop impacts at a predetermined position. In an impulse jet-type printer, the liquid drop of ink is ejected from varying positions of a print nozzle having a plurality of nozzle orifices so the drop impacts directly to the recording medium.
Various problems occur when printing with an electrostatic deflection-type printer or an impulse jet-type printer as follows:
1. The ink dries at the nozzle orifice in view of the minute diameters of 30 to 150 .mu.m causing the nozzle orifice to clog when the viscosity of the ink is high or when the dye separates out from the liquid.
2. The ink takes a long time to dry from the time it first strikes the recording medium.
3. A bubble of air may tend to form in the liquid or along the route to the orifice so that high enough pressure cannot be generated in the pressure chamber of the recording head and a minute drop of ink cannot be expelled from the nozzle orifice.
4. A drop of ink striking the recording paper is not sufficiently round or does not provide sufficient contrast.
In view of these typical problems with ink utilized in an ink jet-type recording device, an improved ink for an ink jet-type recording device should perform as follows:
(a) The ink should not clog the nozzle orifice of the recording head;
(b) the ink should dry as soon as it strikes the recording paper;
(c) the ink should not include any component which generates air;
(d) the quality of the ink should be stable for long periods of time under storage;
(e) the ink should not include any component which corrodes material in contact with the ink; and
(f) the ink should be of sufficiently high density so that the dot produced is round and provides sufficient contrast when the drop impacts the recording medium.
Based on these criteria, it can be seen that there are contradictory physical characteristics sought for a suitable ink for an ink jet-type printer. For example, the ink must be sufficiently slow drying in order not to clog the nozzle orifice as set forth in (a), and must dry shortly after impact upon a print medium or print paper as required in (b). Thus, it has generally been considered difficult to provide an ink for an ink jet-type printer which satisfies all of the criteria set forth in paragraphs (a) to (f), above.
Generally, most of the improvements for meeting the requirements set forth in paragraphs (a) to (f) have been provided by means other than changes in the ink composition. For example, a dryer may be included in a printing device for promptly drying the ink which is applied to the print paper in order to shorten the drying period and satisfy requirements (a) and (b). This is disadvantageous because it increases the size of the printing device. Additionally, it is uneconomical as the dryer consumes additional energy and it limits the type of print paper which can be used in the printing device.
Most of the inks utilized in ink jet-type recording are water-based inks. These water-type based inks generally include three important components, such as a dye, a wetting agent and a water vehicle, but must include two essential components. The dye is an essential component of the ink for providing color so that the dot striking the print paper will transcribe a desired character or figure which is rendered visually distinguishable. Water is the other essential component as it is the medium for carrying the transcribing dye to the recording paper. Thus, the water and dye are the essential components and sufficient for providing an ink which could be used in an ink jet-type recording device.
The nozzle orifice in an ink jet-type device is exposed to air so that the water evaporates causing the dye to separate out in the nozzle thereby clogging the nozzle. In order to prevent this clogging, a wetting agent is added to the ink composition. It is generally known that addition of wetting agent lowers the vapor pressure of the ink as proposed in U.S. Pat. No. 3,889,269. To some extent this prevents the dye from separating out at the nozzle orifice. This reduction in drying solves the clogging problem of (a), but creates a problem under (b) in that the ink does not dry promptly upon impacting the recording paper. In order to overcome this problem and increase drying time, a surface active agent has been added to the three component ink system. The surface active agent decreases the surface tension of the ink so that the ink may penetrate through the recording paper. However, when an ink composition includes a surface active agent, the ink generally penetrates in the random direction of the fibers of the recording paper. When this occurs, the criteria set forth in paragraph (f), above, for providing a high density round dot of sufficient contrast is not attained. That is, the dot is not sufficiently round due to diffusion of the droplet and the quality of the printing suffers.
Accordingly, it is highly desirable to provide an ink which satisfies all of the requirements (a) to (f) set forth above and will be suitable for an ink jet-type recording device. This ink must not clog nozzle oriices, but must also penetrate the recording paper while maintaining the required roundness after the drop strikes the recording paper.